rust/src/lib/fun_treemap.rs

/*
A functional key,value store that works on anything.

This works using a binary search tree. In the first version, it's a
very naive algorithm, but it will probably be updated to be a
red-black tree or something else.

This is copied and modified from treemap right now. It's missing a lot
of features.

*/

import option::some;
import option::none;
import option = option::t;

export treemap;
export init;
export insert;
export find;
export traverse;

tag tree_node<@K, @V> {
    empty;
    node(@K, @V, @tree_node<K, V>, @tree_node<K, V>);
}

type treemap<@K, @V> = @tree_node<K, V>;

fn init<@K, @V>() -> treemap<K, V> { @empty }

fn insert<@K, @V>(m: &treemap<K, V>, k: &K, v: &V) -> treemap<K, V> {
    @alt m {
       @empty. { node(@k, @v, @empty, @empty) }
       @node(@kk, vv, left, right) {
         if k < kk {
             node(@kk, vv, insert(left, k, v), right)
         } else if k == kk {
             node(@kk, @v, left, right)
         } else { node(@kk, vv, left, insert(right, k, v)) }
       }
     }
}

fn find<@K, @V>(m: &treemap<K, V>, k: &K) -> option<V> {
    alt *m {
      empty. { none }
      node(@kk, @v, left, right) {
        if k == kk {
            some(v)
        } else if k < kk { find(left, k) } else { find(right, k) }
      }
    }
}


// Performs an in-order traversal
fn traverse<@K, @V>(m: &treemap<K, V>, f: fn(&K, &V)) {
    alt *m {
      empty. { }
      node(@k, @v, _, _) {
        // copy v to make aliases work out
        let v1 = v;
        alt *m { node(_, _, left, _) { traverse(left, f); } }
        f(k, v1);
        alt *m { node(_, _, _, right) { traverse(right, f); } }
      }
    }
}